Nu Metal came off of Glam Metal and Grunge also came off of Glam Metal. They both have the same roots, so they do sound similar.
To me there's a huge difference between Nu Metal and Grunge. 1. Grunge bands had more of a variety of sounds. Not only apart from other bands but even different sounds within the same band. The was light, shade, heavy, sparse, etc. Nu Metal bands have pretty much one sound and different bands sound similar. 2. Grunge had a lot of power chords, open chords, leads, picking, sometimes all in the same song. Much like 70's bands did. Nu Metal is mostly low power chords. 3. Grunge had a lot of female singers. Nu Metal barely did. 4. If you strip away hip hop from Nu Metal, you get Disturbed. Disturbed is no where near sounding Grunge. They sound Nu Metal without the Hip Hop. I still consider it Nu Metal. 5. I always thought 90's Grunge/Rock was like 70's Rock if you simplified it and added a punk element to it. Nu Metal is like a mix of Korn, Metallica, and Tool except even more simplified. Oh, and Hip Hop too. Something like that anyway. Maybe has an element of Grunge in it too but it not Grunge. 6. Grunge wasn't glam Metal. Glam Metal is like Kiss, Motley Crue, and Poison. Grunge is what put those stupid bands out of style. Grnge was a lot more Punk and had elements of 60's and 70's Rock.
